Control points in NKT-cell development

Cellular Adjuvant Properties, Direct Cytotoxicity of Re-differentiated Vα24 Invariant NKT-like Cells from Human Induced Pluripotent Stem Cells

Vα24 invariant natural killer T (iNKT) cells are a subset of T lymphocytes implicated in the regulation of broad immune responses. They recognize lipid antigens presented by CD1d on antigen-presenting cells and induce both innate and adaptive immune responses, which enhance effective immunity against cancer. Conversely, reduced iNKT cell numbers and function have been observed in many patients with cancer. To recover these numbers, we reprogrammed human iNKT cells to pluripotency and then re-differentiated them into regenerated iNKT cells in vitro through an IL-7/IL-15-based optimized cytokine combination. The re-differentiated iNKT cells showed proliferation and IFN-γ production in response to α-galactosylceramide, induced dendritic cell maturation and downstream activation of both cytotoxic T lymphocytes and NK cells, and exhibited NKG2D- and DNAM-1-mediated NK cell-like cytotoxicity against cancer cell lines. The immunological features of re-differentiated iNKT cells and their unlimited availability from induced pluripotent stem cells offer a potentially effective immunotherapy against cancer.

Discrete TCR Binding Kinetics Control Invariant NKT Cell Selection and Central Priming

Invariant NKT (iNKT) cells develop and differentiate in the thymus, segregating into iNKT1/2/17 subsets akin to Th1/2/17 classical CD4⁺ T cells; however, iNKT TCRs recognize Ags in a fundamentally different way. How the biophysical parameters of iNKT TCRs influence signal strength in vivo and how such signals affect the development and differentiation of these cells are unknown. In this study, we manipulated TCRs in vivo to generate clonotypic iNKT cells using TCR retrogenic chimeras. We report that the biophysical properties of CD1d-lipid-TCR interactions differentially impacted the development and effector differentiation of iNKT cells. Whereas selection efficiency strongly correlated with TCR avidity, TCR signaling, cell-cell conjugate formation, and iNKT effector differentiation correlated with the half-life of CD1d-lipid-TCR interactions. TCR binding properties, however, did not modulate Ag-induced iNKT cytokine production. Our work establishes that discrete TCR interaction kinetics influence iNKT cell development and central priming.

Natural killer T cells in liver injury, inflammation and cancer

The liver is an organ that has the largest amount of natural killer T(NKT) cells, which play critical roles in the pathogenesis of liver diseases. In this article, the authors summarize recent findings about the roles of NKT cells in liver injury, inflammation, fibrosis, regeneration and cancer. In brief, NKT cells accelerate liver injury by producing pro-inflammatory cytokines and directly killing hepatocytes. NKT cells are involved in complex roles in liver fibrogenesis. For instance, NKT cells inhibit liver fibrosis via suppressing hepatic stellate cell activation and can also promote liver fibrosis via enhancing liver inflammation and injury. Inactivated or weakly activated NKT cells play a minimal role in controlling liver regeneration, whilst activated NKT cells have an inhibitory effect on liver regeneration. In liver cancer, NKT cells play both pro-tumor and anti-tumor roles in controlling tumor progress.

Orchestration of invariant natural killer T cell development by E and Id proteins

Natural killer T (NKT) cells are αβ T cells that express a semi-invariant T-cell receptor (TCR) along with natural killer (NK) cell markers and have an innate cell-like ability to produce a myriad of cytokines very quickly upon antigen exposure and subsequent activation. These cells are diverted from conventional single positive (SP) T-cell fate at the double positive (DP) stage, where TCR-mediated recognition of a lipid antigen presented on a CD1d molecule promotes their selection into the NKT lineage. Although many key regulatory molecules have been shown to play important roles in the development of NKT cells, the mechanism of lineage specification and acquisition of effector functions in these cells still remain to be fully addressed. In this review, we specifically discuss the role of a family of class-I helix-loop-helix proteins known as E proteins, and their antagonists Id proteins in NKT celldevelopment. Recent work has shown that these proteins play key roles in invariant NKT (iNKT) development, from the invariant TCR rearrangement to terminal differentiation and maturation. Elucidating these roles provides an opportunity to uncover the transcriptional network that separates NKT cells from concurrently developed conventional αβ T cells.

Roles of TRAF3 in T cells: many surprises

Tumor necrosis factor receptor (TNFR)-associated factor 3 (TRAF3) is broadly involved in different receptor-mediated signaling pathways. Considerable progress was made recently in understanding the role of TRAF3 in T cell biology. Here we review these new findings about how TRAF3 participates in T cell development and function. The different roles of TRAF3 in distinct immune cells are also compared. That TRAF3 is required for T cell effector functions, and invariant Natural Killer T cell function and development, was unexpected. Another surprising finding is that TRAF3 normally restrains regulatory T cell development. It is now clear that TRAF3 regulates signaling to T cells not only through costimulatory members of the TNFR superfamily, but also through the T cell receptor complex, and cytokine receptors. The diverse roles it plays support the multifaceted nature of this molecule. How TRAF3 mediates integration of different signaling cascades is an important topic for future study.

Development of invariant natural killer T cells

Invariant natural killer T (iNKT) cells develop into functionally distinct subsets. Each subset expresses a unique combination of transcription factors that regulate cytokine gene transcription upon activation. The tissue distribution and localization within tissues also varies between subsets. Importantly, the relative abundance of the various subsets is directly responsible for altering several immunological parameters, which subsequently affect the immune response. Here, I review recent advances in our understanding of the molecular regulation of iNKT cell subset development.

Homeostasis of IL-15 dependent lymphocyte subsets in the liver

IL-15 is a member of the gamma chain family of cytokines (γc - CD132). The IL-15 receptor (IL-15R) complex consists of 3 subunits: the ligand-binding IL-15Rα chain (CD215), the β chain (CD122; also used by IL-2), and the common γ chain. The biological activities of IL-15 are mostly mediated by the IL-15:IL-15Rα complex, produced by the same cell and 'trans-presented' to responder cells expressing the IL-15Rβγc. The peculiar and almost unique requirement for IL-15 to be trans-presented by IL-15Rα suggests that the biological effects of IL-15 signaling are tightly regulated even at the level of availability of IL-15. Tissue-specific deletion of IL-15Rα has shown macrophage-and dendritic cell-derived IL-15Rα mediate the homeostasis of different CD8(+) T cell subsets. Here we show that hepatocyte and macrophage- specific expression of IL-15Rα is required to maintain the homeostasis of NK and NKT cells in the liver. Thus, homeostasis of IL-15-dependent lymphocyte subsets is also regulated by trans-presentation of IL-15 by non-hematopoietic cells in the tissue environment.

CDR3β sequence motifs regulate autoreactivity of human invariant NKT cell receptors

Invariant natural killer T (iNKT) cells are a subset of T lymphocytes that recognize lipid ligands presented by monomorphic CD1d. Human iNKT T cell receptor (TCR) is largely composed of invariant Vα24 (Vα24i) TCRα chain and semi-variant Vβ11 TCRβ chain, where complementarity-determining region (CDR)3β is the sole variable region. One of the characteristic features of iNKT cells is that they retain autoreactivity even after the thymic selection. However, the molecular features of human iNKT TCR CDR3β sequences that regulate autoreactivity remain unknown. Since the numbers of iNKT cells with detectable autoreactivity in peripheral blood is limited, we introduced the Vα24i gene into peripheral T cells and generated a de novo human iNKT TCR repertoire. By stimulating the transfected T cells with artificial antigen presenting cells (aAPCs) presenting self-ligands, we enriched strongly autoreactive iNKT TCRs and isolated a large panel of human iNKT TCRs with a broad range autoreactivity. From this panel of unique iNKT TCRs, we deciphered three CDR3β sequence motifs frequently encoded by strongly-autoreactive iNKT TCRs: a VD region with 2 or more acidic amino acids, usage of the Jβ2-5 allele, and a CDR3β region of 13 amino acids in length. iNKT TCRs encoding 2 or 3 sequence motifs also exhibit higher autoreactivity than those encoding 0 or 1 motifs. These data facilitate our understanding of the molecular basis for human iNKT cell autoreactivity involved in immune responses associated with human disease.

Pak2 Controls Acquisition of NKT Cell Fate by Regulating Expression of the Transcription Factors PLZF and Egr2

NKT cells constitute a small population of T cells developed in the thymus that produce large amounts of cytokines and chemokines in response to lipid Ags. Signaling through the Vα14-Jα18 TCR instructs commitment to the NKT cell lineage, but the precise signaling mechanisms that instruct their lineage choice are unclear. In this article, we report that the cytoskeletal remodeling protein, p21-activated kinase 2 (Pak2), was essential for NKT cell development. Loss of Pak2 in T cells reduced stage III NKT cells in the thymus and periphery. Among different NKT cell subsets, Pak2 was necessary for the generation and function of NKT1 and NKT2 cells, but not NKT17 cells. Mechanistically, expression of Egr2 and promyelocytic leukemia zinc finger (PLZF), two key transcription factors for acquiring the NKT cell fate, were markedly diminished in the absence of Pak2. Diminished expression of Egr2 and PLZF were not caused by aberrant TCR signaling, as determined using a Nur77-GFP reporter, but were likely due to impaired induction and maintenance of signaling lymphocyte activation molecule 6 expression, a TCR costimulatory receptor required for NKT cell development. These data suggest that Pak2 controls thymic NKT cell development by providing a signal that links Egr2 to induce PLZF, in part by regulating signaling lymphocyte activation molecule 6 expression.

IL-4 Induced Innate CD8+ T Cells Control Persistent Viral Infection

Memory-like CD8⁺ T cells expressing eomesodermin are a subset of innate T cells initially identified in a number of genetically modified mice, and also exist in wild mice and human. The acquisition of memory phenotype and function by these T cells is dependent on IL–4 produced by PLZF⁺ innate T cells; however, their physiologic function is still not known. Here we found that these IL-4-induced innate CD8⁺ T cells are critical for accelerating the control of chronic virus infection. In CIITA-transgenic mice, which have a substantial population of IL-4-induced innate CD8⁺ T cells, this population facilitated rapid control of viremia and induction of functional anti-viral T-cell responses during infection with chronic form of lymphocytic choriomeningitis virus. Characteristically, anti-viral innate CD8⁺ T cells accumulated sufficiently during early phase of infection. They produced a robust amount of IFN-γ and TNF-α with enhanced expression of a degranulation marker. Furthermore, this finding was confirmed in wild-type mice. Taken together, the results from our study show that innate CD8⁺ T cells works as an early defense mechanism against chronic viral infection.

Over the course of viral infection there may be a limited time period during which the host system can eliminate the virus. When viruses are not eliminated within this period of time, virus can establish persistent infection. Here, we show that IL-4-induced innate CD8⁺ T cells are able to effectively control chronic virus infection. Innate T cells are heterogeneous population of T cells that acquire effector/memory phenotype as a result of their maturation process in thymus, unlike conventional T cells that differentiate into memory cells after antigen encounter in periphery. Previous data suggest that innate T cells might serve as a first-line of defense against certain bacterial pathogens. IL-4-induced innate CD8⁺ T cells are a unique subset of innate T cells that were recently identified in both mouse and human. We found that IL-4-induced innate CD8⁺ T cells immediately accumulated after viral infection and produced a robust amount of effector cytokines. Thereby, IL-4-induced innate CD8⁺ T cells provide an effective barrier to the establishment of persistent infection via effective virus control during the early phase of viral infection. Collectively our data show that IL-4-induced innate CD8⁺ T cells works as an early defense mechanism against chronic viral infection.

mTOR Inhibition Per Se Induces Nuclear Localization of FOXP3 and Conversion of Invariant NKT (iNKT) Cells into Immunosuppressive Regulatory iNKT Cells

CD1d-restricted activation of invariant NKT (iNKT) cells results in the abundant production of various types of cytokines and the subsequent modulation of immune responses. This has been shown to be relevant in several clinical disorders, including cancer, autoimmunity, and graft tolerance. Although it is well known that the suppressive function of regulatory T cells is critically dependent on the FOXP3 gene, FOXP3 can also be expressed by conventional human T cells upon activation, indicating the lack of specificity of FOXP3 as a marker for suppressive cells. In this study, we report that the mammalian target of rapamycin (mTOR) inhibitor rapamycin and IL-10, but not TGF-β, can induce FOXP3 expression in iNKT cell lines. Importantly, however, FOXP3(+) iNKT cells only acquired suppressive abilities when cultured in the presence of the mTOR inhibitor rapamycin. Suppression of responder T cell proliferation by FOXP3(+) iNKT cells was found to be cell contact-dependent and was accompanied by a reduced capacity of iNKT cells to secrete IFN-γ. Notably, imaging flow cytometry analysis demonstrated predominant nuclear localization of FOXP3 in suppressive FOXP3(+) iNKT cells, whereas nonsuppressive FOXP3(+) iNKT cells showed a predominance of cytoplasmically localized FOXP3. In conclusion, whereas IL-10 can enhance FOXP3 expression in iNKT cells, mTOR inhibition is solely required for promoting nuclear localization of FOXP3 and the induction of suppressive FOXP3(+) iNKT cells.

The differential roles of mTOR, ERK, and JNK pathways in invariant natural killer T-cell function and survival

Invariant natural killer T (iNKT) cell is a critical element for both innate and adaptive immunity. The quick responses of mature iNKT cells to TCR stimulation require activation of several different signaling pathways. However, the roles of these signaling pathways in mature iNKT cell biology remain incompletely understood. To address this issue, single signaling pathway was blocked with inhibitor in iNKT cells, and the roles of these signaling pathways were estimated. Results showed that mammalian target of rapamycin (mTOR) plays an essential role for cytokine production and survival in iNKT cells. In contrast, ERK and JNK are more important for iNKT cell effector function, but not survival. Our findings delineate the distinct roles of different signaling pathways in mature iNKT cells and therefore shed new light for modulating iNKT cell function in disease conditions.

Genotype-Associated Differential NKG2D Expression on CD56+CD3+ Lymphocytes Predicts Response to Pegylated-Interferon/Ribavirin Therapy in Chronic Hepatitis C

Hepatitis C virus (HCV) genotype 1 infections are significantly more difficult to eradicate with PEG-IFN/ribavirin therapy, compared to HCV genotype 2. The aim of this work is to investigate the difference of immunological impairments underlying this phenomenon. Pre-treatment NKG2D expression on peripheral CD56+CD3+ lymphocytes and CD56+CD3- NK cells from cases of chronic hepatitis C were analyzed and assessed by treatment effect. Two strains of HCV were used to co-incubate with immune cells in vitro. NKG2D expression on peripheral CD56+CD3+ lymphocytes, but not NK cells, was significantly impaired in genotype 1 infection, compared to genotype 2. When peripheral blood mononuclear cells from healthy donors were co-incubated with TNS2J1, a genotype 1b/2a chimera strain, or with JFH1, a genotype 2a strain, genotype-specific decrease of NKG2D on CD56+CD3+ lymphocytes, but not NK cells, was observed.　Pre-treatment NKG2D expression on peripheral CD56+CD3+ lymphocytes significantly correlated with reduction in serum HCV RNA levels from week 0 to week 4, and predicted treatment response. Ex vivo stimulation of peripheral CD56+CD3+ lymphocytes showed NKG2D expression-correlated IFN-γ production. In conclusion, Decreased NKG2D expression on CD56+CD3+ lymphocytes in chronic HCV genotype 1 infection predicts inferior treatment response to PEG-IFN/ribavirin therapy compared to genotype 2.

Invariant NKT cells require autophagy to coordinate proliferation and survival signals during differentiation

Autophagy regulates cell differentiation, proliferation, and survival in multiple cell types, including cells of the immune system. In this study, we examined the effects of a disruption of autophagy on the differentiation of invariant NKT (iNKT) cells. Using mice with a T lymphocyte-specific deletion of Atg5 or Atg7, two members of the macroautophagic pathway, we observed a profound decrease in the iNKT cell population. The deficit is cell-autonomous, and it acts predominantly to reduce the number of mature cells, as well as the function of peripheral iNKT cells. In the absence of autophagy, there is reduced progression of iNKT cells in the thymus through the cell cycle, as well as increased apoptosis of these cells. Importantly, the reduction in Th1-biased iNKT cells is most pronounced, leading to a selective reduction in iNKT cell-derived IFN-γ. Our findings highlight the unique metabolic and genetic requirements for the differentiation of iNKT cells.

An emerging role for immune regulatory subsets in chronic lymphocytic leukaemia

The last few years has seen the burgeoning of a new category of therapeutics for cancer targeting immune regulatory pathways. Antibodies that block the PD-1/PD-L1 interaction are perhaps the most prominent of these new anti-cancer therapies, but several other inhibitory receptor ligand interactions have also shown promise as targets in clinical trials, including CTLA-4/CD80 and Lag-3/MHC class II. Related to this is a rapidly improving knowledge of 'regulatory' lymphocyte lineages, including NKT cells, MAIT cells, B regulatory cells and others. These cells have potent cytokine responses that can influence the functioning of other immune cells and many researchers believe that they could be effective targets for therapies designed to enhance immune responses to cancer. This review will outline our current understanding of FOXP3+ 'Tregs', NKT cells, MAIT cells and B regulatory cells immune regulatory cell populations in cancer, with a particular focus on chronic lymphocytic leukaemia (CLL). We will discuss evidence linking CLL with immune regulatory dysfunction and the potential for new therapies targeting regulatory cells.

Third-party CD4+ invariant natural killer T cells protect from murine GVHD lethality

Graft-versus-host disease (GVHD) is driven by extensive activation and proliferation of alloreactive donor T cells causing significant morbidity and mortality following allogeneic hematopoietic cell transplantation (HCT). Invariant natural killer T (iNKT) cells are a potent immunoregulatory T-cell subset in both humans and mice. Here, we explored the role of adoptively transferred third-party CD4(+) iNKT cells for protection from lethal GVHD in a murine model of allogeneic HCT across major histocompatibility barriers. We found that low numbers of CD4(+) iNKT cells from third-party mice resulted in a significant survival benefit with retained graft-versus-tumor effects. In vivo expansion of alloreactive T cells was diminished while displaying a T helper cell 2-biased phenotype. Notably, CD4(+) iNKT cells from third-party mice were as protective as CD4(+) iNKT cells from donor mice although third-party CD4(+) iNKT cells were rejected early after allogeneic HCT. Adoptive transfer of third-party CD4(+) iNKT cells resulted in a robust expansion of donor CD4(+)CD25(+)FoxP3(+) regulatory T cells (Tregs) that were required for protection from lethal GVHD. However, in vivo depletion of myeloid-derived suppressor cells abrogated both Treg expansion and protection from lethal GVHD. Despite the fact that iNKT cells are a rare cell population, the almost unlimited third-party availability and feasibility of in vitro expansion provide the basis for clinical translation.

Coupling of T cell receptor specificity to natural killer T cell development by bivalent histone H3 methylation

The fidelity of T cell immunity depends greatly on coupling T cell receptor signaling with specific T cell effector functions. Here, we describe a chromatin-based mechanism that enables integration of TCR specificity into definite T cell lineage commitment. Using natural killer T cells (iNKT cell) as a model of a T cell subset that differentiates in response to specific TCR signaling, we identified a key role of histone H3 lysine 27 trimethylation (H3K27me3) in coupling iNKT cell TCR specificity with the generation of iNKT cells. We found that the Zbtb16/PLZF gene promoter that drives iNKT cell differentiation possesses a bivalent chromatin state characterized by the simultaneous presence of negative and positive H3K27me3 and H3K4me3 modifications. Depletion of H3K27me3 at the Zbtb16/PLZF promoter leads to uncoupling of iNKT cell development from TCR specificity and is associated with accumulation of iNKT-like CD4(+) cells that express a non-iNKT cell specific T cell repertoire. In turn, stabilization of H3K27me3 leads to a drastic reduction of the iNKT cell population. Our data suggest that H3K27me3 levels at the bivalent Zbtb16/PLZF gene define a threshold enabling precise coupling of TCR specificity to lineage commitment.

Genetic engineering of hematopoietic stem cells to generate invariant natural killer T cells

Invariant natural killer T (iNKT) cells comprise a small population of αβ T lymphocytes. They bridge the innate and adaptive immune systems and mediate strong and rapid responses to many diseases, including cancer, infections, allergies, and autoimmunity. However, the study of iNKT cell biology and the therapeutic applications of these cells are greatly limited by their small numbers in vivo (∼0.01-1% in mouse and human blood). Here, we report a new method to generate large numbers of iNKT cells in mice through T-cell receptor (TCR) gene engineering of hematopoietic stem cells (HSCs). We showed that iNKT TCR-engineered HSCs could generate a clonal population of iNKT cells. These HSC-engineered iNKT cells displayed the typical iNKT cell phenotype and functionality. They followed a two-stage developmental path, first in thymus and then in the periphery, resembling that of endogenous iNKT cells. When tested in a mouse melanoma lung metastasis model, the HSC-engineered iNKT cells effectively protected mice from tumor metastasis. This method provides a powerful and high-throughput tool to investigate the in vivo development and functionality of clonal iNKT cells in mice. More importantly, this method takes advantage of the self-renewal and longevity of HSCs to generate a long-term supply of engineered iNKT cells, thus opening up a new avenue for iNKT cell-based immunotherapy.

Ion channels in innate and adaptive immunity

Ion channels and transporters mediate the transport of charged ions across hydrophobic lipid membranes. In immune cells, divalent cations such as calcium, magnesium, and zinc have important roles as second messengers to regulate intracellular signaling pathways. By contrast, monovalent cations such as sodium and potassium mainly regulate the membrane potential, which indirectly controls the influx of calcium and immune cell signaling. Studies investigating human patients with mutations in ion channels and transporters, analysis of gene-targeted mice, or pharmacological experiments with ion channel inhibitors have revealed important roles of ionic signals in lymphocyte development and in innate and adaptive immune responses. We here review the mechanisms underlying the function of ion channels and transporters in lymphocytes and innate immune cells and discuss their roles in lymphocyte development, adaptive and innate immune responses, and autoimmunity, as well as recent efforts to develop pharmacological inhibitors of ion channels for immunomodulatory therapy.

The route to pathologies in chronic inflammatory diseases characterized by T helper type 2 immune cells

T helper type 2 (Th2)-characterized inflammatory responses are highly dynamic processes initiated by epithelial cell damage resulting in remodelling of the tissue architecture to prevent further harm caused by a dysfunctional epithelial barrier or migrating parasites. This process is a temporal and spatial response which requires communication between immobile cells such as epithelial, endothelial, fibroblast and muscle cells and the highly mobile cells of the innate and adaptive immunity. It is further characterized by a high cellular plasticity that enables the cells to adapt to a specific inflammatory milieu. Incipiently, this milieu is shaped by cytokines released from epithelial cells, which stimulate Th2, innate lymphoid and invariant natural killer (NK) T cells to secrete Th2 cytokines and to activate dendritic cells which results in the further differentiation of Th2 cells. This milieu promotes wound-healing processes which are beneficial in parasitic infections or toxin exposure but account for increasingly dysfunctional vital organs, such as the lung in the case of asthma and the colon in ulcerative colitis. A better understanding of the dynamics underlying relapses and remissions might lead ultimately to improved therapeutics for chronic inflammatory diseases adapted to individual needs and to different phases of the inflammation.

Frequencies of circulating IL-17-producing CD4+CD161+ T cells and CD4+CD161+ T cells correlate with disease activity in rheumatoid arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is a common autoimmune disease that is primarily driven by effector T cells, particularly Th17 cells, which are mainly contained within CD4+CD161+ T cells. Thus, we aimed to explore whether the frequencies of circulating IL-17-producing CD4+CD161+ T cells and CD4+CD161+ T cells were correlated with RA disease activity.

METHODS

The surface phenotype and cytokine production of blood were analyzed by flow cytometry in 52 RA patients and 17 healthy controls. The disease activity was evaluated by the 28-joint disease activity score.

RESULTS

The frequencies of circulating IL-17-producing CD4+CD161+ T cells and CD4+CD161+ T cells were increased in RA patients, and they were elevated in patients with active disease status compared to patients with low disease status. Furthermore, their frequencies were positively correlated with disease activity parameters. Receiver operating characteristic curve analysis revealed that IL-17-producing CD4+CD161+ T cell levels were able to distinguish disease activity with 60.7 % sensitivity and 87.5 % specificity, while CD4+CD161+ T cell levels showed 92.9 % sensitivity and 66.7 % specificity.

CONCLUSION

These results support the hypothesis that Th17 cells are involved in the pathogenesis of RA and suggest that circulating CD4+CD161+ T cells are a potential biomarker of RA disease activity.

Invariant natural killer T cells regulate anti-tumor immunity by controlling the population of dendritic cells in tumor and draining lymph nodes

BACKGROUND

Invariant natural killer T (iNKT) cells are CD1d-restricted T cells, which respond rapidly to antigen recognition and promote development of anti-tumor immunity in many tumor models. Surprisingly, we previously found that mice deficient in iNKT cells developed spontaneous CD8(+) T cells responses partially effective at inhibiting metastases in mice bearing the 4T1 mammary carcinoma, and showed a markedly improved response to treatment with local radiotherapy and anti-CTLA-4 antibody compared to wild type (WT) mice.

METHODS

To understand the mechanisms of the immunosuppressive function of iNKT cells, dendritic cells (DCs) were analyzed by immunohistochemistry and flow cytometry in WT and iNKT-deficient (iNKT(-/-)) mice. The effects of antibody-mediated blockade of CD1d on DC number and phenotype, priming of anti-tumor T cells, and tumor response to treatment with local radiotherapy and anti-CTLA-4 antibody were evaluated. To determine if the improved response to treatment in the absence of iNKT cells was independent from the immunotherapy employed, 4T1-tumor bearing WT and iNKT(-/-) mice were treated with local radiotherapy in combination with antibody-mediated CD137 co-stimulation.

RESULTS

DCs in 4T1 tumors and tumor-draining lymph nodes but not distant lymph nodes were significantly reduced in WT mice compared to iNKT(-/-) mice (p < 0.05), suggesting the selective elimination of DCs cross-presenting tumor-associated antigens by iNKT cells. Consistently, priming of T cells to a tumor-specific CD8 T cell epitope in mice treated with radiotherapy and anti-CTLA-4 or anti-CD137 was markedly enhanced in iNKT(-/-) compared to WT mice. CD1d blockade restored the number of DC in WT mice, improved T cell priming in draining lymph nodes and significantly enhanced response to treatment.

CONCLUSIONS

Here we describe a novel mechanism of tumor immune escape mediated by iNKT cells that limit priming of anti-tumor T cells by controlling DC in tumors and draining lymph nodes. These results have important implications for the design of immunotherapies targeting iNKT cells.

Evolution of nonclassical MHC-dependent invariant T cells

TCR-mediated specific recognition of antigenic peptides in the context of classical MHC molecules is a cornerstone of adaptive immunity of jawed vertebrate. Ancillary to these interactions, the T cell repertoire also includes unconventional T cells that recognize endogenous and/or exogenous antigens in a classical MHC-unrestricted manner. Among these, the mammalian nonclassical MHC class I-restricted invariant T cell (iT) subsets, such as iNKT and MAIT cells, are now believed to be integral to immune response initiation as well as in orchestrating subsequent adaptive immunity. Until recently the evolutionary origins of these cells were unknown. Here we review our current understanding of a nonclassical MHC class I-restricted iT cell population in the amphibian Xenopus laevis. Parallels with the mammalian iNKT and MAIT cells underline the crucial biological roles of these evolutionarily ancient immune subsets.

Therapeutic implications of CD1d expression and tumor-infiltrating macrophages in pediatric medulloblastomas

Immunobiology of medulloblastoma (MB), the most common malignant brain tumor in children, is poorly understood. Although tumor cells in some MBs were recently shown to express CD1d and be susceptible to Vα24-invariant natural killer T (NKT)-cell cytotoxicity, the clinical relevance of CD1d expression in MB patients remains unknown. We investigated the expression of CD1d in pediatric MBs and correlated with molecular and clinical characteristics. Specifically, we explored if NKT cell therapy can be targeted at a subset of pediatric MBs with poorer prognosis. Particularly, infantile MBs have a worse outcome because radiotherapy is delayed to avoid neurocognitive sequelae. Immunohistochemistry for CD1d was performed on a screening set of 38 primary pediatric MBs. Gene expression of the membrane form of M2 macrophage marker, CD163, was studied in an expanded cohort of 60 tumors. Outcome data was collected prospectively. Thirteen of 38 MBs (34.2 %) expressed CD1d on immunohistochemistry. CD1d was expressed mainly on MB tumor cells, and on some tumor-associated macrophages. Majority (18/22, 82 %) of non sonic-hedgehog/Wingless-activated MBs (group 3 and 4) were CD1d-negative (p = 0.05). A subset of infantile MBs (4/9, 44.4 %) expressed CD1d. Macrophages infiltrating MB expressed CD163 apart from CD1d. Molecular subtypes demonstrated statistical differences in CD163 expression, SHH-tumors were the most enriched (p = 0.006). Molecular and clinical subtypes of pediatric MB exhibit distinct differences in CD1d expression, which have important therapeutic implications. High CD1d expression in infantile MBs offers potential new immunotherapeutic treatment with NKT cell therapy in infants, where treatment is suboptimal due delayed radiotherapy.

Natural killer T cells: drivers or passengers in preventing human disease?

Natural killer T (NKT) cells are credited with regulatory roles in immunity against cancers, autoimmune diseases, allergies, and bacterial and viral infections. Studies in mice and observational research in patient groups have suggested that NKT cell-based therapies could be used to prevent or treat these diseases, yet the translation into clinical settings has been disappointing. We support the view that NKT cells have regulatory characteristics that could be exploited in clinical settings, but there are doubts about the natural roles of NKT cells in vivo and whether NKT cell defects are fundamental drivers of disease in humans. In this Opinion article, we discuss the uncertainties and opportunities regarding NKT cells in humans, and the potential for NKT cells to be manipulated to prevent or treat disease.

Mammalian target of rapamycin complex 1 orchestrates invariant NKT cell differentiation and effector function

Invariant NKT (iNKT) cells play critical roles in bridging innate and adaptive immunity. The Raptor containing mTOR complex 1 (mTORC1) has been well documented to control peripheral CD4 or CD8 T cell effector or memory differentiation. However, the role of mTORC1 in iNKT cell development and function remains largely unknown. By using mice with T cell-restricted deletion of Raptor, we show that mTORC1 is selectively required for iNKT but not for conventional T cell development. Indeed, Raptor-deficient iNKT cells are mostly blocked at thymic stage 1-2, resulting in a dramatic decrease of terminal differentiation into stage 3 and severe reduction of peripheral iNKT cells. Moreover, residual iNKT cells in Raptor knockout mice are impaired in their rapid cytokine production upon αGalcer challenge. Bone marrow chimera studies demonstrate that mTORC1 controls iNKT differentiation in a cell-intrinsic manner. Collectively, our data provide the genetic evidence that iNKT cell development and effector functions are under the control of mTORC1 signaling.

A prominent role for invariant T cells in the amphibian Xenopus laevis tadpoles

Invariant T (iT) cells expressing an invariant or semi-invariant T cell receptor (TCR) repertoire have gained attention in recent years because of their potential as specialized regulators of immune function. These iT cells are typically restricted by nonclassical MHC class I molecules (e.g., CD1d and MR1) and undergo differentiation pathways distinct from conventional T cells. While the benefit of a limited TCR repertoire may appear counterintuitive in regard to the advantage of the diversified repertoire of conventional T cells allowing for exquisite specificity to antigens, the full biological importance and evolutionary conservation of iT cells are just starting to emerge. It is generally considered that iT cells are specialized to recognize conserved antigens equivalent to pathogen-associated molecular pattern. Until recently, little was known about the evolution of iT cells. The identification of class Ib and class I-like genes in nonmammalian vertebrates, despite the heterogeneity and variable numbers of these genes among species, suggests that iT cells are also present in ectothermic vertebrates. Indeed, recent studies in the amphibian Xenopus have revealed a drastic overrepresentation of several invariant TCRs in tadpoles and identified a prominent nonclassical MHC class I-restricted iT cell subset critical for tadpole antiviral immunity. This suggests an important and perhaps even dominant role of multiple nonclassical MHC class I-restricted iT cell populations in tadpoles and, by extension, other aquatic vertebrates with rapid external development that are under pressure to produce a functional lymphocyte repertoire with small numbers of cells.

Invariant natural killer T cells: boon or bane in immunity to intracellular bacterial infections?

Invariant natural killer T (iNKT) cells represent a specialized subset of innate lymphocytes that recognize lipid and glycolipid antigens presented to them by nonclassical MHC-I CD1d molecules and are able to rapidly secrete copious amounts of a variety of cytokines. iNKT cells possess the ability to modulate innate as well as adaptive immune responses against various pathogens. Intracellular bacteria are one of the most clinically significant human pathogens that effectively evade the immune system and cause a myriad of diseases of public health concern globally. Emerging evidence suggests that iNKT cells can confer immunity to intracellular bacteria but also inflict pathology in certain cases. We summarize the current knowledge on the contribution of iNKT cells in the host defense against intracellular bacterial infections, with a focus on the underlying mechanisms by which these cells induce protective or pathogenic reactions including the pathways of direct action (acting on infected cells) and indirect action (modulating dendritic, NK and T cells). The rational exploitation of iNKT cells for prophylactic and therapeutic purposes awaits a profound understanding of their functional biology.

The bacterial pathogen Listeria monocytogenes and the interferon family: type I, type II and type III interferons

Interferons (IFNs) are secreted proteins of the cytokine family that regulate innate and adaptive immune responses to infection. Although the importance of IFNs in the antiviral response has long been appreciated, their role in bacterial infections is more complex and is currently a major focus of investigation. This review summarizes our current knowledge of the role of these cytokines in host defense against the bacterial pathogen Listeria monocytogenes and highlights recent discoveries on the molecular mechanisms evolved by this intracellular bacterium to subvert IFN responses.

Invariant NKT cell development: focus on NOD mice

Natural killer T (NKT) cells are non-conventional T lymphocytes expressing a TCRαβ and several NK cell markers. Once activated, they can rapidly secrete large amounts of cytokines such as IFN-γ and IL-4. As a result they can favor both Th1 and Th2 immune responses and play a critical role in anti-pathogenic immune responses as well as in regulation of autoimmune diseases. It has now been clearly established that iNKT cells can be subdivided into three subpopulations: iNKT1, iNKT2 and iNKT17 cells. Each of these populations is characterized by the expression of a particular transcription factor, surface markers and cytokines making them functionally distinct. Interestingly, NOD mice developing autoimmune diabetes exhibit a high frequency of iNKT17 cells, which can participate in the disease.

NF-κB control of T cell development

The NF-κB signal transduction pathway is best known as a major regulator of innate and adaptive immune responses, yet there is a growing appreciation of its importance in immune cell development, particularly of T lineage cells. In this Review, we discuss how the temporal regulation of NF-κB controls the stepwise differentiation and antigen-dependent selection of conventional and specialized subsets of T cells in response to T cell receptor and costimulatory, cytokine and growth factor signals.

Runt-related transcription factor 3 is involved in the altered phenotype and function in ThPok-deficient invariant natural killer T cells

The interplay between the CD4-lineage transcription factor ThPok and the CD8-lineage transcription factor, runt-related transcription factor 3 (Runx3), in T-cell development has been extensively documented. However, little is known about the roles of these transcription factors in invariant natural killer T (iNKT) cell development. CD1d-restricted iNKT cells are committed to the CD4(+)CD8(-) and CD4(-)CD8(-) sublineages, which respond to antigen stimulation with rapid and potent release of T helper (Th) 1 and Th2 cytokines. However, previous reports have demonstrated a new population of CD8(+) NKT cells in ThPok-deficient mice. In the current study, we sought to determine whether Runx3 was involved in the re-expression of CD8 and function of iNKT cells in the absence of ThPok. We used mice lacking Runx3, ThPok or both and verified that Runx3 was partially responsible for the appearance of CD8(+) iNKT cells in ThPok knockout mice. Additionally, Runx3 participated in the immune response mediated by iNKT cells in a model of α-galactosylceramide-induced acute hepatitis. These results indicate that Runx3 is crucial for the phenotypic and functional changes observed in ThPok-deficient iNKT cells.

Polyclonal type II natural killer T cells require PLZF and SAP for their development and contribute to CpG-mediated antitumor response

CD1d-restricted natural killer T (NKT) cells are innate-like T cells with potent immunomodulatory function via rapid production of both Th1 and Th2 cytokines. NKT cells comprise well-characterized type I NKT cells, which can be detected by α-galactosylceramide-loaded CD1d tetramers, and less-studied type II NKT cells, which do not recognize α-galactosylceramide. Here we characterized type II NKT cells on a polyclonal level by using a Jα18-deficient IL-4 reporter mouse model. This model allows us to track type II NTK cells by the GFP(+)TCRβ(+) phenotype in the thymus and liver. We found type II NKT cells, like type I NKT cells, exhibit an activated phenotype and are dependent on the transcriptional regulator promyelocytic leukemia zinc finger (PLZF) and the adaptor molecule signaling lymphocyte activation molecule-associated protein (SAP) for their development. Type II NKT cells are potently activated by β-D-glucopyranosylceramide (β-GlcCer) but not sulfatide or phospholipids in a CD1d-dependent manner, with the stimulatory capacity of β-GlcCer influenced by acyl chain length. Compared with type I NKT cells, type II NKT cells produce lower levels of IFN-γ but comparable amounts of IL-13 in response to polyclonal T-cell receptor stimulation, suggesting they may play different roles in regulating immune responses. Furthermore, type II NKT cells can be activated by CpG oligodeoxynucletides to produce IFN-γ, but not IL-4 or IL-13. Importantly, CpG-activated type II NKT cells contribute to the antitumor effect of CpG in the B16 melanoma model. Taken together, our data reveal the characteristics of polyclonal type II NKT cells and their potential role in antitumor immunotherapy.

Polymorphisms in the CD1d promoter that regulate CD1d gene expression are associated with impaired NKT cell development

CD1d-restricted NKT cells comprise an innate-like T cell population that exerts significant influence over early events in the developing immune response. The frequency of NKT cells is highly variable in humans and in mice, but the basis for this variability remains unclear. In this study, we report a striking deficiency of type I NKT cells in the wild-derived inbred strains PWD/PhJ, SPRET/EiJ, and CAST/EiJ. Investigation of the underlying basis for the lack of type I NKT cells revealed that one strain, PWD/PhJ, exhibited a significant impairment in thymocyte and splenocyte CD1d gene and protein expression. Accordingly, both thymocytes and bone marrow-derived dendritic cells from PWD mice exhibited a significant impairment in the ability to present α-galactosylceramide to NKT cells. The impaired PWD CD1d gene expression was due to impaired CD1d promoter activity. Fine-mapping of the promoter activity revealed that two single nucleotide substitutions at positions -331 and -164 in the proximal promoter were each sufficient to account for the diminished PWD CD1d promoter activity. Examination of the strain distribution pattern of these polymorphisms revealed that, of 19 strains analyzed, only PWD and PWK mice possessed both CD1d promoter polymorphisms. A subsequent examination of the PWK strain revealed that it also exhibited impaired thymocyte CD1d expression and very low numbers of NKT cells. Taken together, these results provide new insight into the control of CD1d gene expression, and they have implications for the evolution of CD1d and type I NKT cells.

Increased level of E protein activity during invariant NKT development promotes differentiation of invariant NKT2 and invariant NKT17 subsets

E protein transcription factors and their natural inhibitors, Id proteins, play critical and complex roles during lymphoid development. In this article, we report that partial maintenance of E protein activity during positive selection results in a change in the cell fate determination of developing iNKT cells, with a block in the development of iNKT1 cells and a parallel increase in the iNKT2 and iNKT17 subsets. Because the expression levels of the transcription factors that drive these alternative functional fates (GATA-3, RORγT, T-bet, and Runx-3) are not altered, our results suggest that E protein activity controls a novel checkpoint that regulates the number of iNKT precursors that choose each fate.

Combined deletion of Id2 and Id3 genes reveals multiple roles for E proteins in invariant NKT cell development and expansion

The invariant NKT (iNKT) cells represent a unique group of αβ T cells that have been classified based on their exclusive usage of the invariant Vα14Jα18 TCRα-chain and their innate-like effector function. Thus far, the transcriptional programs that control Vα14Jα18 TCRα rearrangements and the population size of iNKT cells are still incompletely defined. E protein transcription factors have been shown to play necessary roles in the development of multiple T cell lineages, including iNKT cells. In this study, we examined E protein functions in T cell development through combined deletion of genes encoding E protein inhibitors Id2 and Id3. Deletion of Id2 and Id3 in T cell progenitors resulted in a partial block at the pre-TCR selection checkpoint and a dramatic increase in numbers of iNKT cells. The increase in iNKT cells is accompanied with a biased rearrangement involving Vα14 to Jα18 recombination at the double-positive stage and enhanced proliferation of iNKT cells. We further demonstrate that a 50% reduction of E proteins can cause a dramatic switch from iNKT to innate-like γδ T cell fate in Id2- and Id3-deficient mice. Collectively, these findings suggest that Id2- and Id3-mediated inhibition of E proteins controls iNKT development by restricting lineage choice and population expansion.

Role of diacylglycerol kinases in T cell development and function

Diacylglycerol (DAG), a second messenger generated by phospholipase Cγ1 activity upon engagement of a T-cell receptor, triggers several signaling cascades that play important roles in T cell development and function. A family of enzymes called DAG kinases (DGKs) catalyzes the phosphorylation of DAG to phosphatidic acid, acting as a braking mechanism that terminates DAG-mediated signals. Two DGK isoforms, α and ζ, are expressed predominantly in T cells and synergistically regulate the development of both conventional αβ T cells and invariant natural killer T cells in the thymus. In mature T cells, the activity of these DGK isoforms aids in the maintenance of self-tolerance by preventing T-cell hyperactivation upon T cell receptor stimulation and by promoting T-cell anergy. In CD8 cells, reduced DGK activity is associated with enhanced primary responses against viruses and tumors. Recent work also has established an important role for DGK activity at the immune synapse and identified partners that modulate DGK function. In addition, emerging evidence points to previously unappreciated roles for DGK function in directional secretion and T-cell adhesion. This review describes the multitude of roles played by DGKs in T cell development and function and emphasizes recent advances in the field.

CD28 controls the development of innate-like CD8+ T cells by promoting the functional maturation of NKT cells

NK T cells(NKT cells) share functional characteristics and homing properties that are distinct from conventional T cells. In this study, we investigated the contribution of CD28 in the functional development of γδ NKT and αβ NKT cells in mice. We show that CD28 promotes the thymic maturation of promyelocytic leukemia zinc finger(+) IL-4(+) NKT cells and upregulation of LFA-1 expression on NKT cells. We demonstrate that the developmental defect of γδ NKT cells in CD28-deficient mice is cell autonomous. Moreover, we show in both wild-type C57BL/6 mice and in downstream of tyrosine kinase-1 transgenic mice, a mouse model with increased numbers of γδ NKT cells, that CD28-mediated regulation of thymic IL-4(+) NKT cells promotes the differentiation of eomesodermin(+) CD44(high) innate-like CD8(+) T cells. These findings reveal a previously unappreciated mechanism by which CD28 controls NKT-cell homeostasis and the size of the innate-like CD8(+) T-cell pool.

DOCK8 is critical for the survival and function of NKT cells

Patients with the dedicator of cytokinesis 8 (DOCK8) immunodeficiency syndrome suffer from recurrent viral and bacterial infections, hyper-immunoglobulin E levels, eczema, and greater susceptibility to cancer. Because natural killer T (NKT) cells have been implicated in these diseases, we asked if these cells were affected by DOCK8 deficiency. Using a mouse model, we found that DOCK8 deficiency resulted in impaired NKT cell development, principally affecting the formation and survival of long-lived, differentiated NKT cells. In the thymus, DOCK8-deficient mice lack a terminally differentiated subset of NK1.1(+) NKT cells expressing the integrin CD103, whereas in the liver, DOCK8-deficient NKT cells express reduced levels of the prosurvival factor B-cell lymphoma 2 and the integrin lymphocyte function-associated antigen 1. Although the initial NKT cell response to antigen is intact in the absence of DOCK8, their ongoing proliferative and cytokine responses are impaired. Importantly, a similar defect in NKT cell numbers was detected in DOCK8-deficient humans, highlighting the relevance of the mouse model. In conclusion, our data demonstrate that DOCK8 is required for the development and survival of mature NKT cells, consistent with the idea that DOCK8 mediates survival signals within a specialized niche. Accordingly, impaired NKT cell numbers and function are likely to contribute to the susceptibility of DOCK8-deficient patients to recurrent infections and malignant disease.

Genetic control of murine invariant natural killer T cells maps to multiple type 1 diabetes regions

Reduced frequency of invariant natural killer T (iNKT)-cells has been indicated as a contributing factor to type 1 diabetes (T1D) development in NOD mice. To further understand the genetic basis of the defect, we generated (NOD X ICR)F2 mice to map genes that control iNKT-cell development. We determined frequencies of thymic and splenic iNKT-cells as well as the ratio of CD4-positive and -negative subsets in the spleens of 209 F2 males. Quantitative trait loci (QTL) analysis revealed 5 loci that exceed the significant threshold for the frequency of thymic and/or splenic iNKT-cells on Chromosomes (Chr) 1, 5, 6, 12, and 17. Three significant loci on Chr 1, 4, and 5 were found for the ratio of CD4-positive and -negative splenic iNKT-cells. Comparisons to previously known mouse T1D susceptibility (Idd) loci revealed two significant QTL peak locations respectively mapped to Idd regions on Chr 4 and 6. The peak marker location of the significant Chr 12 iNKT QTL maps to within 0.5Mb of a syntenic human T1D locus. Collectively, our results reveal several novel loci controlling iNKT-cell development and provide additional information for future T1D genetic studies.

TNF receptor associated factor 3 plays a key role in development and function of invariant natural killer T cells

Loss of TRAF3 results in reduced TCR signaling and defective up-regulation of T-bet and CD122 in iNKT cells that impairs their proliferation and survival.

TCR signaling is a prerequisite for early stage development of invariant natural killer T (iNKT) cells, whereas IL-15 signaling is required for expansion and maturation at later stages. In this study, we show that TNF receptor associated factor 3 (TRAF3) plays a critical role in the transition between these two distinct signaling pathways and developmental stages. TRAF3-deficient iNKT cells in CD4^CreTRAF3^flox/flox (T-TRAF3^−/−) mice exhibit defective up-regulation of T-bet and CD122, two critical molecules for IL-15 signaling, and as a consequence, IL-15–mediated iNKT cell proliferation and survival are impaired. Consistently, development of iNKT cells in T-TRAF3^−/− mice shows a major defect at developmental stages 2 and 3, but not stages 0 and 1. We further demonstrated that defective T-bet up-regulation occurring during the stage 1 to stage 2 transition results from reduced TCR signaling in TRAF3^−/− iNKT cells. In addition, mature TRAF3^−/− iNKT cells displayed defective cytokine responses upon TCR stimulation. Collectively, our results reveal that by modulating the relative strength of TCR signaling, TRAF3 is an important regulator of iNKT cell development and functions.

Impaired autophagy, defective T cell homeostasis, and a wasting syndrome in mice with a T cell-specific deletion of Vps34

Autophagy plays a critical role in multiple aspects of the immune system, including the development and function of T lymphocytes. In mammalian cells, the class III PI3K vacuolar protein sorting (Vps)34 is thought to play a critical role in autophagy. However, recent studies have cast doubt on the role of Vps34 in autophagy, at least in certain cell types. To study the effects of Vps34 on autophagy in T lymphocytes, we generated mice that selectively lack Vps34 in the T cell lineage. Vps34 ablation in T cells caused profound defects in autophagic flux, resulting in accumulation of cellular organelles and apoptosis. These animals exhibited normal intrathymic development of conventional T cells, but they were profoundly impaired in the intrathymic development of invariant NKT cells. In peripheral organs, T cell-specific ablation of Vps34 had a profound impact on T cell homeostasis and function. Furthermore, aged animals developed an inflammatory wasting syndrome characterized by weight loss, intestinal inflammation, and anemia. Consistent with this phenotype, Vps34 was required for the peripheral maintenance and function of CD4(+)Foxp3(+) regulatory T cells. Collectively, our study reveals a critical role for Vps34 in autophagy and for the peripheral homeostasis and function of T lymphocytes.

Frequencies of circulating IL-17-producing CD4+CD161+ T cells and CD4+CD161+ T cells correlate with disease activity in rheumatoid arthritis

OBJECTIVE: Rheumatoid arthritis (RA) is a common autoimmune disease that is primarily driven by effector T cells, particularly Th17 cells, which are mainly contained within CD4+CD161+ T cells. Thus, we aimed to explore whether the frequencies of circulating IL-17-producing CD4+CD161+ T cells and CD4+CD161+ T cells were correlated with RA disease activity. METHODS: The surface phenotype and cytokine production of blood were analyzed by flow cytometry in 52 RA patients and 17 healthy controls. The disease activity was evaluated by the 28-joint disease activity score. RESULTS: The frequencies of circulating IL-17-producing CD4+CD161+ T cells and CD4+CD161+ T cells were increased in RA patients, and they were elevated in patients with active disease status compared to patients with low disease status. Furthermore, their frequencies were positively correlated with disease activity parameters. Receiver operating characteristic curve analysis revealed that IL-17-producing CD4+CD161+ T cell levels were able to distinguish disease activity with 60.7 % sensitivity and 87.5 % specificity, while CD4+CD161+ T cell levels showed 92.9 % sensitivity and 66.7 % specificity. CONCLUSION: These results support the hypothesis that Th17 cells are involved in the pathogenesis of RA and suggest that circulating CD4+CD161+ T cells are a potential biomarker of RA disease activity.

Agonist-selected T cell development requires strong T cell receptor signaling and store-operated calcium entry

T cell receptor (TCR) signaling driven by interaction of the TCR with specific complexes of self-peptide and the major histocompatibility complex determines T cell fate in thymic development. However, the signaling pathway through which TCR signal strength regulates distinct T cell lineages remains unknown. Here we have used mice lacking the endoplasmic reticulum Ca2+ sensors stromal interaction molecule 1 (STIM1) and STIM2 to show that STIM-induced store-operated Ca2+ entry is not essential for thymic development of conventional TCRαβ+ T cells but is specifically required for the development of agonist-selected T cells (regulatory T cells, invariant natural killer T cells, and TCRαβ+ CD8αα+ intestinal intraepithelial lymphocytes). The severe impairment of agonist-selected T cell development is mainly due to a defect in interleukin-2 (IL-2) or IL-15 signaling. Thus, STIM1 and STIM2-mediated store-operated Ca2+ influx, leading to efficient activation of NFAT (nuclear factor of activated T cells), is critical for the postselection maturation of agonist-selected T cells.

Induced IL-17-producing invariant NKT cells require activation in presence of TGF-β and IL-1β

IL-17 production by innate-like lymphocytes, including γδ and invariant NKT (iNKT) cells, have been ascribed to specific lineages that are endowed with this functional specialization during thymic differentiation. IL-17-producing iNKT cells have been described as a CD4(-)NK1.1(-) lineage in mice and CD161(+) in humans. We found that, in mice, noncommitted iNKT cells can be induced to produce IL-17 when activated in presence of TGF-β and IL-1β. This peripheral induction of IL-17 expression could be observed in any subset irrespectively of CD4 and NK1.1 expression, the process leading to loss of NK1.1 expression and partial CD4 downmodulation. Furthermore, induced IL-17-producing iNKT cells were sufficient to drive neutrophilic airways inflammation upon intratracheal adoptive cell transfer into congenic mice. Taken together, our data show that similarly to regulatory T cells, which have a natural and peripherally induced subset, IL-17 production by iNKT cells can also be imprinted in natural iNKT17 cells or peripherally induced.

The Tec kinase ITK regulates thymic expansion, emigration, and maturation of γδ NKT cells

The Tec family tyrosine kinase, Itk, regulates signaling downstream of the TCR. The absence of Itk in CD4(+) T cells results in impaired Th2 responses along with defects in maturation, cytokine production, and survival of iNKT cells. Paradoxically, Itk(-/-) mice have spontaneously elevated serum IgE levels, resulting from an expansion of the Vγ1.1(+)Vδ6.3(+) subset of γδ T cells, known as γδ NKT cells. Comparisons between γδ NKT cells and αβ iNKT cells showed convergence in the pattern of cell surface marker expression, cytokine profiles, and gene expression, suggesting that these two subsets of NKT cells undergo similar differentiation programs. Hepatic γδ NKT cells have an invariant TCR and are derived predominantly from fetal progenitors that expand in the thymus during the first weeks of life. The adult thymus contains these invariant γδ NKT cells plus a heterogeneous population of Vγ1.1(+)Vδ6.3(+) T cells with diverse CDR3 sequences. This latter population, normally excluded from the liver, escapes the thymus and homes to the liver when Itk is absent. In addition, Itk(-/-) γδ NKT cells persistently express high levels of Zbtb16 (PLZF) and Il4, genes that are normally downregulated in the most mature subsets of NKT cells. These data indicate that Itk signaling is required to prevent the expansion of γδ NKT cells in the adult thymus, to block their emigration, and to promote terminal NKT cell maturation.